1. Technical Field of the Invention
This invention relates to radio telecommunication systems and, more particularly, to a system and method of statistically multiplexing a plurality of digitized data or packetized voice calls on one or more intersystem transmission circuits utilizing frame relay techniques.
2. Description of Related Art
Existing radio telecommunications networks are capable of supporting circuit-mode data services within the framework of existing air interface technologies such as, for example, Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA). In order to support circuit-mode data services and packetized voice services, an interworking function (IWF) is added to the anchor Base Station (BS) or anchor Mobile Switching Center (MSC) (i.e., the system on which the call initially sets up). The IWF translates between the specialized digital radio link protocols and fixed landline-based modems, terminals, and facsimile machines. The IWF assigned to a particular call to a mobile station remains fixed in the anchor MSC as the mobile station hands off to other serving systems. This supports seamless operation and eliminates the need to pass complex call-state information as the mobile station moves from one MSC to another.
In order to facilitate the implementation of the IWF in the anchor system, an Intersystem Link Protocol (ISLP) transports data frames over an E-interface between a serving MSC and an anchor MSC, and rate adapts the radio link protocol rate to intersystem facility rates, for example 64 kbps Digital Stream 0 (DS0). An ISLP is currently being standardized in PN3660 for the intersystem signaling standard IS-41 (ANSI-41) by a EIA/TIA TR45.2 working group, and the ballot has been approved. The PN3660-ISLP is applicable to the TDMA (IS-136) Digital Advanced Mobile Phone System (D-AMPS) and to CDMA (IS-95) systems as well. The PN3660-ISLP merely frames higher level Radio Link Protocol (RLP) frames and performs inter-frame fill utilizing High-Level Datalink Control (HDLC)-based flags. This process is described in PN3660 and call delivery and handoff signaling additions to ANSI-41 described in PN3770, both of which are hereby incorporated by reference herein. The GSM system also has an ISLP which performs similar functions based on the ITU standard V.110. The GSM-ISLP is described in GSM 04.21 version 4.6.0 which is hereby incorporated by reference herein.
Neither the PN3660-ISLP nor the GSM-ISLP support multiplexing of a plurality of calls on a single intersystem transmission circuit. Therefore, both the PN3660-ISLP and the GSM-ISLP require one intersystem trunk per intersystem data call.
Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, U.S. Pat. No. 4,987,570 to Almond et al. (Almond) discusses subject matter that bears some relation to matters discussed herein. Almond discloses a method and apparatus for performing time-interleaved, multiplexed rate adaptation for sub-rate channels in a digital communication system. Almond improves bandwidth utilization by packaging sub-rate channel data into fragment-size envelopes of smaller size than the channel capacity which are then time-interleaved on available channels to improve the system's bandwidth usage. Almond performs time-interleaved multiplexed rate adaptation with a fragment size ideally equal to the granularity of the system's switch. For example, a 2.048 Mb (non-multiplexed) channel is divided into 32 slots of 64 Kb each. Each slot contains eight fragments of 8 Kb, the smallest channel size that can be switched through the system.
However, Almond addresses only landline communications, and does not teach or suggest a method of multiplexing a plurality of data calls on multiple intersystem transmission circuits in a radio telecommunication system. Additionally, Almond does not suggest the use of frame relay which permits variable length fragments to be utilized, nor does Almond suggest statistical multiplexing on the channel.
Review of each of the foregoing references reveals no disclosure or suggestion of a system or method such as that described and claimed herein.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have an intersystem link protocol which enables multiple data calls to be placed on the same trunk. By utilizing frames of variable length and statistically multiplexing the channels, most, if not all, of the available bandwidth is utilized. Such a protocol would provide a more efficient intersystem (inter-MSC) transport protocol capable of supporting circuit-mode data services such as Asynchronous Data Services (ADS), Group 3 Facsimile (G3 Fax), and packetized voice. The present invention provides such a protocol.